Discharge rectifier tube with indirectly heated cathode



July 14, 1942. P. H. CRAIG ET AL 2,289, 346

DISCHARGE RECTIFIER TUBE WITH INDIRECTLY HEATED CATHODE Fil ed May 31, 1940 2 Sheets-Sheet 1 ,5, INVENTOR. 7,29 Pad n er M Cra/y July 14, 1942. P. H. CRAIG 'ETAL DISCHARGE RECTIFIER TUBE WITH INDIRECTLY HEATED CATHODE Filed May 31, 1940 2 Sheets-Sheet 2 INVENTOR B/mer Cra/g BY (/0617 6/0061 I Patented July 14, 1942 UNITED STATES PATENT OFFICE DISCHARGE RECTIFIER. TUBE WITH INDIRECTLY HEATED CATI'IODE L Palmer H. Craig, Shaker Heights, and JolmJ. Glauber, Cleveland Heights, Ohio, assignors to Invex Corporation, a corporation of New York Application May 31, 1940, Serial No. 338,194

8 Claims.

envelope, improved means for conducting the main discharge current through the cathode and out of the tube, and for conducting current for heating the cathode to and from cathode heating elements;

To provide an electronic tube of the space discharge rectifler'class, constructed in an improved manner whereby improved qualities of cheapness The tube of this invention, therefore, comprises in general an evacuated envelope containing an anode, and an indirectly heated cathode, and ionizable gas at predetermined pressure; and, when control of the current flow through the tube is wanted, a control electrode or grid. In the preferred construction, the grid, when employed, is in the form of a loop or band externally encircling or embracing the envelope, but the grid may be of other forms, and may be disposed within the envelope.

It is therefore among the objects of the present invention:

To provide generally an improved electronic tube of the gaseous discharge rectifier class and of the type having a hot cathode;

To provide generally an improved electronic tube of the class referred to, and of the type having an indirectly heated cathode and a control electrode or grid;

To provide an improved construction of indirectly heated cathode for electronic'tubes;

To provide for electronic tubes of the type having a cathode indirectly heated'by electric current, improved means for reducing heat radiation from the heated parts of the cathode, whereby the necessary wattage to attain a desired cathode temperature may be minimized.

To provide, in an indirectly heated cathode of the type comprising a heated, two-dimensional metal surface having thermionic material thereon, an improved construction whereby a metal surface of great area maybe contained in a small three-dimensional space; i

To provide in a tube of the type referred to, an improved construction and arrangement of control grid;

Toprovide, in a tube of the evacuated-envelope directly-heated-cathode type, improved means for mounting and supporting the cathode structure'on a pinch of the tube,

To provide, in a tube of the hot cathode gaseof manufacture and reliability and emciency in operation are attained.

Other objects will be apparent to those skilled in the art to which our invention appertains.

Our invention is fully disclosed in the following description taken in connection with the accompanying drawings, in which:

Fig. 1 is a front elevational view of a tube embodying our invention with a part of the envelope broken away to disclose internal parts of the tube; I

Fig. 2 is a view to enlarged scale partly in longitudinal section of a cathode of the tube of Fig. 1; i

Fig. 3 is a vi w taken from the plane 3-3 of Fig. 2;

Fig. 4 is a view to reduced scale taken in the direction of the arrow 4 of Fig. 2;

Fig. 5 is a view, in some respects diagram-. matic, illustrating th *"ernal construction of the cathode of Fig. 2; i

Fig. 6 is a CI'DSS-SBCtIOBL view taken from the plane 6-6 of Fig. 2;

Fig. 7 is a diagrammatic view illustrating an a 0 with three insulated prongs, 5 and 6, and havu an anode I electrically connected to an external terminal 9 in the usual manner. The anode may be of graphite, or of molybdenum, or of carbonized nickel, or may be of other materials such as have been used for the anodes of tubes of the hot cathode rectifier type.

At I0 is shown generally a cathode of the inous discharge rectifier type having an evacuated directly heated type. structurally it comprises,

see Fig. 2, a pair of posts II and I2 extending upwardly from the pinch and spot welded to pposite portions of a main outer cathode cylinder I3 of nickel or other suitable metal. For convenience of assembling, the posts are in two parts, the lower parts l4 and I5, being mounted -and sealed in the pinch I, and having sleeves I6 and I1 welded thereto, and the upper parts, the posts II and I2 proper, being telescoped into the sleeves I6 and I I to mount the posts on the pinch.

By this means, the cathode structure proper, including the posts II and I2, may be separately constructed, and the post parts I4 and I5 with their sleeves I6 and I1, may be mounted in the pinch I; and subsequently the cathode structure may be mounted on the pinch by telescoping the posts proper II and I2 into the sleeves I6 and I1. Inasmuch as the posts proper II and I2 may, if desired, be themselves extended to include the parts I4 and I5 and be integral therewith and mounted in the pinch, hereinafter the posts, including the sleeves I6 and I1 and the post parts I4 and I5, are referred to as the posts II and I2, for convenience of description.

Within the cylinder I3 and co-axial therewith is an inner metal tube I8, see Figs. 5 and 6. A plurality of heater tubes I9, 20, 2|, and 22, are disposed between the inner wall of the cylinder I3 and the outer wall of the inner tube I8 and spot-welded to the tubes I3 and I8 at opposite points on the heater tubes. The cross-sectional form of the inner tube I8 is preferably polygonal, although this is not essential, and it may be of square cross-section as shown, or of hexagonal or octagonal section, and the planar portions of such a polygonal tube provide convenient means for positioning the heater tubes I9 to 22 and the outer tube I3 around a common axis of the cathode as illustrated.

A post 23 mounted in and extending upwardly from the pinch I has its upper end disposed in a socket or thimble 24 secured by welding to a lower outer sheet metal head 25 having an upwardly extending skirt 26 at its periphery. A lower inner sheet metal head 21, likewise pro- 33 of the upper head 3I, and the shield 35 Is povided with a peripheral skirt 28, rests upon the head and is preferably spaced therefrom to reduce heat conduction through the head 25, by

means of pimples or bosses 29 pressed outwardly downwardly from the metal of the head 21 and resting upon the head 25.

Perforations 30-30 are provided in the head through which the said posts II and I2 extend and thereby the heads are positioned relative to the posts.

The outer tube I3, inner tube I8, and heater tongues 34-34 bent upwardly from the periphery of the perforation 32, and spot welded to the "posts II and I2 at their upper end portions. The

perforation 32 in the upper head is preferably of approximately the size and shape of the outer tube I3 and aligned therewith.

Heat insulating tubes or shields 35 and 36, of low heat-conducting material, such for example as lava, are provided mounted independently of sitioned by prongs 31 bent downwardly from the head 3|. The inner shield 35 is spaced from the tube I3 and entirely out of contact therewith, and the outer shield 36 is spaced from the inner shield, thereby providing complete tubular heat insulating spaces therewithin.

Below the cathode proper thus constructed, a ring 38 is supported by being welded to a post 39 mounted in the pinch. Heating filaments 40, 4|, 42, 43, arranged to be electrically heated, and wound into helical form, are disposed axially of and within the heater tubes I 9 to 22, their lower ends being axially extended through perforations in the lower heads and spot welded to the ring .38, and their upper ends being axially extended out of the cathode proper and spot welded to tongues 44 extending upwardly from the upper head 3I at the periphery of the perforation 32.

A reflector 45 of nickel or like metal and in the form of a disc, is mounted above the cathode proper by tongues 46-46 bent downwardly from opposite edges thereof and spot welded to the upper ends of the posts II and I2, preferably to the tongues 34-34.

The reflector 45 reduces heat radiation axially away from the cathode proper, and together with the heat insulation effected by the shields 35 and 36 as described reduces the total radiation of heat and enables the filaments 40 to 43 to maintain the desired temperature of the oathode at the expenditure of correspondingly small wattage.

By the construction above described, a great sheet metal cathode surface area is provided in small three-dimensional space, and this surface area is coated with thermionic material such as barium or strontium carbonate or a mixture thereof, which, when the cathode surfaces are heated in the process of evacuating the tube as is customary (either inductive, by means of a high frequency coil, or conductively, by current caused to flow into and out ofgthe structure by way of the posts II and I2, or b'yboth means), is converted into strontium or barium oxide or a mixture thereof. This oxide coating of thermionic materialis shown in Fig. 6 at 41 on the inner wall of the outer tube I3, and at 48 on the outer walls of the heating tubes I9 to 22, and at "on the outer wall of the inner tube I8, and at 59 on the inner wall of the tube I8. The electric circuit to heat the filaments is from a wire 5| to the post 39, see Fig. 2, to which is connected the ring 38, thence to all of the filaments 49 to 43 in parallel to the upper head 3|, and thence through the post II and out by a wire 52.

A getter pellet is shown at 53, Fig. 1, mounted on a wire 54 welded to one of the sleeves, such for example as the sleeve H, which is flashed in the usual manner during the usual process of evacuating the envelope, which may be employed.

The main circuit through the tube is from the anode connection 9 to the anode 8, through the gase as a discharge are to the cathode outer tube I3, and thence by post I2 to a wire 55. The wires 5|, 52 and 55, shown 'best in Fig. 2, are, as will be understood from prior tube practice, connected to the insulated prongs 4, 5 and 6 of the cathode proper above described. They rest Fig. 1.

evacuated by the well known process, including heating of the -internalstructural parts and flashing of the getter; and then gas, such as .The filaments heat the saidtubes and their thermionic coatings, causing the latter to emit electrons, and these electrons ionize the gas within the envelope causing it to emit other eleca,ase,s4e

As referred to above, the envelope may be" trons; and when potential is impressed upon the an external band-grid outside of and embracingor encircling the envelope I, is provided, and it may be variously constructed. It may be in the form of a separate metal detachable wire or band of metal; or a band of metal mesh; but preferably we provide a band which in efiect is sealed ,into the material of the outer wall of the envelope. The preferred process for applying such a band grid is that used'in ornamentlng glass ware with bands or the like of platinum. A socalled liquid platinum is painted in the form of a band on the outer wall of the envelope and over an, outwardly extending nipple 51. The glass and the band are then heated and the band fuses into the glass surface under the band, the

band having finally the appearance of being a part of the glass. A band thus made is conductive, and a terminal 58 is mounted on that part of the band covering the nipple by which electric connection can be made to the grid. The band being fused to the glass cannot shift. If the band 56 be considered as a separate detachable metal band, its conformity with the glass projection or nipple 51 interlocks it with the envelope and prevents it from shifting out of position axially of the envelope.

The grid is shown in Fig. 1 as disposed between the cathode and anode which is its preferred position.

When a tube constructed as-above described is put into operation by heating the filaments ing current, such a tube admits of control of the effective amperage flowing, by suitablyenergizing the grid, inasmuch as the grid can at any time be energized to cut off the flow of current by preventing its starting on the next succeeding positive half cycle; or by lower degrees of energization can control the eifective amperage by delaying the time of starting in each positive half cycle.

Because of the greater usefulness of the tube with. alternating current, as above indicated, it is considered herein onlyin that usage.

A more stable and otherwise satisfactory control' of the amperage flowing through the tube may be effected if alternating voltage is impressed upon the grid and out of phase with that impressed upon the anode and cathode. To this end the control of the effective amperage by corresponding energization of the grid may be effected by varying the phase relationship between the grid energization and the potential impressed upon the anode; but wexprefer to effect this control by utilizing a fixed angular phase displacement of the grid energization and varying the potential on the midst this phase displacement. We have found that a suitable phase displacement is approximately 135 degrees lag of band grid negative potential behind the anode positive potential, and this fixed-angle, variablepotential grid control is fully illustrated anddescribed in the patent to Palmer H. Craig, No. 2,001,836, issued May 21, 1935, to which reference may be had.

In Fig. 7 is illustrated a representative circuit for effecting this type of control with a tube such as is described above. In this figure, at I is shown the envelope, at 8 the anode, at 56 the grid, at II and [2 the posts supporting the oathode l3,, I8, 20 to 22, heated by filaments 40 to 43. Supply mains 59 and 60 energize the primary SI of a transformer, the secondary 62 of which supplies alternating current at suitable sistor 65 and a condenser 66, the said loop circuit A being also connected to the supply main 5!! by a thereof, discharge tends to fiow in theform of an positive sign, it is with the meaning that it is positive with respect to the cathode; and when the grid is referred to as negative it is with the meaning that it is negative with respect to the anode when the latter is positive. 1

When the potential impressed upon the anode and cathode is alternating, the how of current occurs only during those half waves in which the anode is positive as is well known, and, even without energizationof the grid, is automaticab ly interrupted in each half cycle in which the anode i negative; and therefore with alternatwire 61.

The grid 56 is connected "at 58 to the resistor 65 by an adjustable rheostat type of connection for adjusting the potential ofthe grid 56, the circuitfor the grid being considered as from the connection 58 to the grid thence to the anode 8, through the wire 51 and back to apart of i the resistor 65. The condenser 65 may be ad- 56 may be adjusted by theadjustable connection 68.

As illustrative of, suitable quantities for parts of the circuit of Fig. 7, we may add here that for a rectifier as described above having a continuous main current carrying capacity of 2% amperes, the capacity of the condenser 65 may suitably be .019 microfarad and the resistance of the resistor 65 may suitably be of the order of 150,000 ohms, and the voltage across the resistor provided by the transformer secondary 64 may suitaby be 600 volts for supply mains at volts 60 cycles. with the fixed phase displacement referred to, the grid connection at I! may be adjusted from for zero grid potential, at which the full 2 /2 amperes will flow in the main load circuit, from the anode to the cathode of the tube; and that if the potential or the grid 58 be ad- Justed to raise it, the effective amperage in the load circuit will .be decreased, and at approximately 450 volts on the grid 56, the main current will be completely cut oil. It follows that the eifective current supplied to the load of Fig. 7 can be adjustablyvaried from zero to the maximum capacity of the tube by adjusting the connection at 68.

As mentioned hereinbefore, rectifier tubes of the gaseous discharge type are known containing a gas such as argon in the envelope. In the above described tube, we also prefer to employ as stated a gas such as argon, but we have found that the pressure of the gas within the envelope should be taken into account. For any pressure utilized the grid energization should correspond, when the control of the current flow by the grid energization is wanted. If a low gas pressure is used, the grid voltage to normally cut of! current flow is lower, and if the pressure is high, it is higher.

We have found that, taking into account the voltage drop and loss of energy through the tube, and the optimum control conditions for varying aaeasac the scope of our invention without sacrificing its advantages and within the scope of the app nded claims. For example the tube of our invention may be used in multiple back-to-back arrangement, to .pass a full wave of alternating current.

We claim:

1. An indirectly heated cathode structure comsheet metal tube, a group of sheet metal tubes the current by the grid from zero to the maximum discharge current of the tube, a suitable pressure is of the order of 90 to 110 microns of mercury, and we therefore prefer to use that pressure of argon in the tube for ordinary application. i

In alternating current installations in which variation of the flow of current through the tube is not wanted, and all that is wanted is initiation and interruption of the current by grid control, the negative grid may be energized with a phase displacement of 180 degrees with respect to the positive anode. Also while we have described the control of variation of the current flow through the tube .by utilizing a negative grid energized out of phase with the positive anode and having the grid potential adjusted by a rheostat .at a fixed phase displacement, it is to be understood that our invention may likewise be practiced by the above mentioned system which adjusts the phase displacement of the grid energization with respect to the anode potential. It is believed that these alternative methods of practicing our invention will be understood from the more complete description of the preferred methods without further illustration or description herein.

We have described our tube herein as simply a tube of the rectifier class, the discharge amperage through which may be controlled by controlling the grid voltage. The tube of the construction illustrated and described herein, but operating as a light responsive or photo-electric tube, constitutes the subject matter of the co-pending application of Palmer H. Craig and Lester C. Herman, Serial Number 334,846, filed May 13, 1940, assigned to the same assignee as the present application, the tube of said co-pending application being named Photodyne. When the gird is not utilized, or. if provided, when it is not engergized, the tube operates as a simple rectifier tu Our invention is not limited to the exact details of construction illustrated and described. Changes and modifications may be made within within the outer sheet metal tube, thermionic coatings on the outer walls of the group of tubes and on the inner wall of the outer tube, a plurality of heaters within at least some of the tubes of the group, and electrically connected in parallel at one end to a post, and at the other end electrically connected to a common conductor.

3. An indirectly heated cathode structure comprising an inner metal tube, a plurality of metal tubes thermo-conductively engaged with the Outer surface of the inner tube, and spaced from each other, an outer metal tube telescoped over and thermo-conductively engaged with the outer walls of the plurality of tubes thereby providing a plurality of passages the walls of which are walls of the inner, outer and plurality of tubes, a coating of thermionic material on the walls of the passages, and heating means for heating the walls of the passages.

4. An indirectly heated cathode structure comprising an inner metal tube, a plurality of metal tubes thermo-conductively engaged with the tubes, a coating of thermionic material on the walls of the passages, and heaters disposed coaxially within the plurality of tubes respectively for heating the walls of the passages.

5. An indirectly heated cathode construction comprising a pair of spaced-apart sheet metal tubes, a heater extending axially within each tube and spaced from its inner wall, a walled passageway between the tubes the outer walls of said tubes being walls of said passageway and a thermionic coating on the passageway walls.

6. An indirectly heated cathode construction comprising outer and inner coaxial tubes and an intermediate tube thermo-conductively engaged with the outer and inner tubes, a thermionic coating on the inner and outer surfaces of the outer and inner tubes respectively and on the outer wall of the intermediate tube and a heater extending axially within the intermediate tube. I

7. An' indirectly heated cathode construction comprising upper and lower sheet metal. heads, an outer, an inner and a plurality of intermediate sheet metal tubes between the heads disposed to provide walled passages between adjacent in ported by the posts, an

termediate tubes, the passage walls being coated with thermionic material, heating elements within the intermediate tubes for heating the coated walls, and a tubular wall of heat insulating material surrounding and spaced from the outer sheet metal tube and supportedby the said heads.

8. An indirectly heated cathode construction comprising a pair of spaced apart supporting posts, upper and lowersheet metal heads supouter tube between the heads, a plurality of sheet metal tubes within the outer tube spaced to provide walled passages therebetween, the walls of the passages being coated with thermionic material, heating means for heating the coated walls, a tubular wall of heat insulating material surrounding and spaced from the outer tube and supported between the heads, an opening in the upper'head aligned with the outer tube and a heat reflector supported in axially spaced relation with respect to and transversely substantially coextensive with w the opening in the upper head.

PALMER H. CRAIG. JOHN J. GLAUBER. 

